In terms of steel, strength and ductility are inversely related, and the following technologies according to the related art are used as methods of obtaining steel having excellent strength and ductility.
As representative examples, there are technologies of controlling a phase fraction of a ferrite, bainite, or martensite structure such as dual phase (DP) steel disclosed in Korean Patent Publication No. 0782785, transformation induced plasticity (TRIP) steel disclosed in Korean Patent Publication No. 0270396, as well as controlling a residual austenite fraction by utilizing an alloying element such as manganese (Mn), nickel (Ni), or the like disclosed in Korean Patent Publication No. 1054773.
However, in a case of DP steel or TRIP steel, increases in strength are limited to 1200 MPa. In addition, in the case of a technology of controlling a residual austenite fraction, increases in strength are limited to 1200 MPa, and there may be a problem of increased manufacturing costs due to the addition of a relatively expensive alloying element.
Thus, the development of a steel in which relatively expensive alloying elements may be used in significantly reduced amounts and excellent strength and ductility may be provided is required.